1. Field of the Invention
The present invention relates to a circuit breaker designed to limit the current by actuating a movable contact with an electromagnetic repulsion resulting from the flow of high currents regardless of the tripping operation of an automatic tripping device.
2. Description of the Related Art
In general, circuit breakers of the above-described design are known in the technical field of prior art. Construction and operation of a typical circuit breaker will now be described with reference to FIGS. 1 through 6.
FIG. 1 a longitudinal sectional side view of the circuit breaker; FIG. 2 is an enlarged view of a major part of the breaker shown in FIG. 1 showing the ON state; FIG. 3 is the same view as FIG. 2 showing the OFF state; FIG. 4 is the same view as FIG. 2 showing the TRIP state; FIG. 5 is the same view as FIG. 2 showing the REPULSION state; and FIG. 6 is a partly longitudinal enlarged view of FIG. 5. In FIGS. 1 through 6, reference numeral 1 is a circuit breaker case. The circuit breaker case comprises a base 1a and a cover 1b. 2 is a fixed conductor on the power supply side securely mounted on the base 1a; 3 designates a fixed contact fixedly attached to the fixed conductor 2; 4 is an automatic tripping device; 5 indicates a fixed conductor on the load side connected to the automatic tripping device 4; 6 is a movable contact; 7 represents a movable contact arm on which the movable contact 6 is fixed attached; 8 designates a flexible conductor for connecting the movable contact arm 7 to the automatic tripping device 4 via a connecting conductor 9; and 10 designates a contact arm holding the movable contact arm 7, which is divided into a first contact arm 10a connected with a switching mechanism (will be described later) and a second contact arm 10b rotatably supporting the movable contact arm 7 by a first pin 11. 12 indicates a support shaft of the contact arm 10, which rotatably supports the first contact arm 10a and the second contact arm 10b. 13 indicates a cross bar connecting the first contact arm 10a of each pole; 14 designates a guide hole provided in the first contact arm 10a and extending toward opening and closing the contacts; and 15 designates a long hole provided in the second contact arm 10b and extending in the direction intersecting the guide hole 14. 16 is a second pin fitted in both the guide hole 14 and the long hole 15; and 17 designates a tension spring provided between the first pin 11 and the second pin 16, constantly pulling the second pin 16. 18 is a contact pressure spring provided between the movable contact arm 7 and the second contact arm 10b; 19 designates a circuit breaker operating handle; and 20 represents a circuit breaker switching mechanism comprising a cradle 20a, an upper link 20b and a lower link 20c. 21 designates a stopper pin provided on the cradle 20a; 22 is a connecting pin for connecting the lower link 20c to the first contact arm 10a; and 23 indicates an arc-extinguishing chamber.
Next, the operation of this circuit breaker will be explained. In the ON state shown in FIGS. 1 and 2, the current flows in the direction of the fixed conductor 2 on the power supply side, the fixed contact 3, the movable contact 6, the movable contact arm 7, the flexible conductor 8, the connecting conductor 9, the automatic tripping device 4 and the fixed conductor 5 on the load side in order of mention. When the operating handle 19 is operated to the OFF position (in the direction of the arrow 24 in FIG. 2), the contact arm 10 is raised by the switching mechanism 20, thus moving the movable contact 6 together with the movable contact arm 7 away from the fixed contact 3 as shown in FIG. 3. At this time, as the second pin 16 is held in a recess 14a of the guide hole 14 by the tension spring 17, the second contact arm 10b is raised together with the first contact arm 10a by the switching mechanism 20, turning on the center of a support shaft 12 up until it hits a stopper pin 21 and stops.
When an overload current flows in the ON state shown in FIGS. 1 and 2, the automatic tripping device 4 operates to turn the cradle 20a in the direction of the arrow 25 in FIG. 2 and the switching mechanism 20 operates to raise the contact arm 10, thus opening the movable contact 6 to interrupt the overload current as shown in FIG. 4. That is, the device comes in a so-called "trip state". As the second pin 16 is held in the recess 14a of the guide hole 14 by the tension spring 17 as in the case of the OFF state in FIG. 3, the second contact arm 10b, together with the first contact arm 10a, is raised by the switching mechanism 20, turning on the center of the support shaft 12 until it hits against the stopper pin 21 and stops.
If a high current, such as a short-circuit current, flows in the ON state shown in FIGS. 1 and 2, the movable contact arm 7 repulses the fixed conductor 2 by the action of an electromagnetic force produced between the fixed conductor 2 and the movable contact arm 7, opening the contacts as shown in FIG. 5. At this time, as the operation of the first contact arm 10a actuated by the switching mechanism 20 which operates in succession to the operation of the automatic tripping device 4 delays in time, the second contact arm 10b overcomes the force of the tension spring 17, releasing the second pin 16 from the recess 14a. Therefore the second pin 16 will move along the guide hole 14, allowing the second contact arm 10b to turn on the center of the support shaft 12 to open in the direction of a third arrow 26. The second pin 16, therefore, will hit against the end 14b of the guide hole 14 and stop. This repulsive motion is faster than the operation of the switching mechanism 20 to which the movable contact arm 7 is connected through the contact arm 10, thereby enhancing the current limiting effect. The first contact arm 10a is tripped by the automatic tripping device 4 successively to the repulsive state in FIG. 5 and raised, and therefore the second pin 16 will go again into the recess 14a of the guide hole 14, presenting the trip state shown in FIG. 4. This operation is called as "the reset of the contact arm 10". At this time, the second pin 16, being pulled by the tension spring 17, makes one reciprocating motion on the pin slide surface 15a of the long hole 15 with its contact surface 16a in contact with the pin sliding surface 15c of the guide hole 14.
In conventional circuit breakers described above, the first contact arm 10a, the second contact arm 10b and the second pin 16 are plated for rust prevention or produced of stainless metals. Accordingly, there occurs a great deal of frictional resistance between the contact surface 16a of the second pin and both the sliding surfaces 14c and 15a (see FIG. 2) when the second pin 16 slides in the guide hole 14 and the long hole 15, resulting in a decrease in the operating speed. Therefore, there is such a problem that a lowered circuit breaker performance results, and a considerable force will be required for resetting after the breaking of circuit.
The present invention has been accomplished in an attempt to solve the above-described problem, and accordingly, it is a first object of the present invention to provide a circuit breaker having an improved performance obtained by increasing its operating speed through the reduction of the frictional resistance between both the pin sliding surfaces of the guide hole and the long hole and the contact surface of the second pin and also a decreased resetting load after circuit interrupting.
Furthermore, in the conventional circuit breakers, the first contact arm 10a, the second contact arm 10b and the second pin 16 are galvanized for rust prevention purposes. There, however, is such a problem that, because of its low melting temperature, zinc used in this galvanizing melts, allowing such molten metals as molten copper and silver alloy to hold on the pin sliding surface 14c of the guide hole 14, the pin sliding surface 15a of the long hole 15, and the contact surface 16a of the second pin 16, and accordingly resulting in poor movement of the second pin 16 and a failure in obtaining a stabilized circuit breaking performance.
The present invention has been accomplished to solve this problem, and therefore it is a second object of the present invention to provide a circuit breaker capable of preventing the poor movement of the second pin and, accordingly, obtaining a stabilized circuit breaking performance by preventing arc-molten metals from attaching on both the pin sliding surfaces of the guide hole and the long hole and the contact surface of the second pin.
In the conventional circuit breakers described above, since the second pin 16 is engaged with both the guide hole of the first contact arm 10a and the long hole 15 of the second contact arm 10b (see FIG. 6), the pin sliding surface 14c of the guide hole 14 and the pin sliding surface 15a of the long hole 15 receive an impact force of the second pin 16 when the circuit breaker opens and closes. Because of an occurrence of this impact force, the second pin 16 will make a dent in both the pin sliding surfaces 14c and 15a, resulting in unsmooth movement of the second pin 16 itself and accordingly, in unstable circuit breaking performance.
The present invention has also been accomplished in an attempt to solve the above-described problem, and therefore has a third object to provide a circuit breaker having a stabilized circuit breaking performance without the formation of dents in both the pin sliding surfaces of the guide hole and the long hole by the second pin and accordingly, without the unsmooth movement of the second pin.